Comparative somatostatin receptor scintigraphy using In-111-DOTA-lanreotide and In-111-DOTA-Tyr(3)-octreotide versus F-18-FDG-PET for evaluation of somatostatin receptor-mediated radionuclide therapy

Background: Based on the high number of somatostatin (SST) receptors expres sed by neuroendocrine tumors, long-acting SST analogs have been successfull y used for tumor detection. New developments point to the potential use of these types of radioligands for tumor-specific radionuclide therapy. Patients and methods: We have comparatively investigated the diagnostic cap acity of the SST analog, In-111-DOTA-lanreotide (LAN), as opposed to In-111 -DOTA-DPhe(1)-Tyr(3)-octreotide (TOCT) in tumor patients. This article give s an overview of recent scintigraphic results compared to CT/MRI, F-18-FDG- PET, endoscopy and/or surgery in a threshold of 218 tumor patients. Results: As opposed to radiology, previously unknown tumor lesions were dem onstrable by either SST radioligand in about one third of patients. In carc inoid patients, the SST scan sensitivity was 64% for LAN (18 of 28) and 87% (34 of 39) for TOCT, whereas the sensitivity was 100% in patients with (ra dioiodine-negative) thyroid cancer (17 of 17) for LAN and 95% for TOCT (20 of 21). Discordant scintigraphic results between LAN and TOCT (higher tumor uptake and/or visualisation of different lesions in the same patient) were also seen in patients with lymphoma, lung cancer and intestinal adenocarci noma. In a direct comparison of both SST tracers in 38 tumor patients, LAN gave positive results in 35 of 38, TOCT in 36 of 38 and 18F-FDG-PET in 14 o f 22 of the same patients. SST scan results obtained by both tracers were e quivocal in 23 of 38 patients, but were better in 10 patients with TOCT and in 5 patients with LAN. Conclusions: We conclude that both SST radioligands are suitable tracers fo r tumor imaging, but may give significantly different uptake results for di fferent tumor types. Since the uptake is most important for tumor therapy, using either long-acting SST analogs, and/or Y-90-labeled analogs, careful evaluation should be made prior to therapy.